As is known, medical devices at present in use for treatment of kidney problems, and especially for extracorporeal blood treatment, are constituted by complex apparatus which internally comprise hydraulic circuits for managing the various patient treatment operations.
By way of mere non-exhaustive example, dialysis machines at present in use comprise a blood circuit destined to remove blood from the patient and to bring it to a treatment unit. Once treated the blood is returned to the patient. In general, the above-described circuit is accompanied by a preparation line of a treatment fluid which brings a dialyser liquid into a situation of exchange with the blood inside the treatment unit, the exchange enabling an interaction between dialyser liquid and blood so as to achieve the desired treatment effect.
Apart from the above-mentioned blood line and dialyser liquid preparation line, there might also be circuits destined to enable effecting of preparation of other liquids, such as medical or replacement liquids, as well as further circuits or lines for discharging the used liquid, for the control of ultrafiltration, or other lines, safety lines and/or washing lines which further increase the complexity and number of circuits internally of the machine. Each medical device for dialysis operations internally comprises a plurality of tubes and connections for the tubes, destined for transporting fluids of varying natures and under different flow and pressure conditions which are also variable over periods of time.
The presence of electronic apparatus for management and control, as well as motors and moving mechanical parts in the machines means that the problem of sealing and reliability of the hydraulic circuits is seen to be of particular and primary importance.
Clearly the most critical area in the hydraulic plants is the connections present in the actual fluid lines.
At present, usual dialysis machines, to join two or more tubes, use connections made of elastomeric materials, such as, for example, silicone. Generally these connectors are constituted by a main body internally affording a channel which the fluid crosses.
The tubes are directly connected to the connectors and the connector joints are achieved by friction coupling. The friction forces generated between the smooth internal surface of the connector and the tube are strong enough to guarantee fluid seal and mechanical seal of the hydraulic circuit.
This type of connector, though widespread in use in the sector, is however subject to improvement under certain of its aspects.
Firstly, an important observation is that hydraulic circuits in dialysis machines are subject to high quantities of fluid flow.
Generally speaking the movement of the fluid is obtained, in this type of machine, by using pumps, for example gear pumps or peristaltic pumps, which by their nature create non stationary flow conditions inside the hydraulic circuit; the flows produced are characterised by the presence of series of repeated and successive pressure peaks, which can also be non-cyclic in nature.
The particular types of treatment to be performed, but also the washing and sterilising operations on the circuits themselves, lead to flow conditions inside the circuitry which are such as to generate considerable stress thereon, especially at the connections and especially when flow is inverted.
Because of the above, it is not an infrequent occurrence that after repeated cycles the tube end portions can detach from the connectors, causing exit of liquids contained therein.
This can lead to serious problems during treatment of a patient, but can also have dire consequences for the electrical or electronic apparatus which the machine is equipped with.
Document EP645161 describes a variable-section straight connector having removable portions for connecting tubes having different diameters.
Document EP 1262703 teaches a connector for non-medical use devices which connects coaxial tubes having different sections. The connector is provided with ribbing at the connecting ends.
Furthermore it is obvious that even simple changes in relative positions between the tube and the connector can lead to an imperfect fluid seal, with the attendant risk that fluid can leak out and damage the apparatus.